Instrumentation for fluid coking of heavy hydrocarbon oils and the like



1958 M. A. SEGURA 2,856,346

INSTRUMENTATION FOR FLUID COKING 0F HEAVY HYDROCARBON 0113s AND THE LIKE Filed July 21, 1953 *HEATER 55 zs A \-n H 5 571 65 8' 9 M 23 .wfl/ 67 9 [1 \TO INSTRUMENT 6! 83 FIGURE-2 L, STRIPPER- 33 FIGURE-I 43 Marne A. Segura m m United States Patent Ofiice 2,856,346 Patented :Oct. 14, 1958 INSTRUMENTATION F'DR FLUID COKING OF HEAVY HYDROCARBON OILS AND THE LIKE Marnell A. Segura, Baton Rouge, La., assignor to Essa Research and Engineering Company, a corporation of Delaware Application July 21, 1953, Serial No. 369,473

2 Claims. (Cl. 208-48) The present invention relates to improvements in instrumentation for fluid coking of heavy hydrocarbon oils and the like. The invention is particularly applicable to instruments which are adapted to record and control pressure and fluid flow conditions inside coking apparatus where deposits of coke and the like tend to build up.

In the conversion of heavy hydrocarbon oils by thermal treatment or coking, there is a tendency for a considerable proportion of the feed to be degraded to coke. Some of this coke tends to deposit upon the equipment, although by proper design such deposits may be minimized or greatly reduced.

In processes where feed and flow rate, etc., are to be controlled automatically, it is obviously essential that the control or recording instruments reflect and/or react to the actual conditions within the apparatus. In a fluid solids bed reactor, for example, where heavy hydrocarbon oils are converted by contact with preheated particulate solids, such as finely divided coke or other solids, it is necessary to control feed rates, gas flow rates, solids transfer, etc., in accordance with the conditions in the system. Pressure differentials between two or more points, temperature conditions, bed levels, fluidizing gas flow rates, etc., must be sensed and recorded. When one or more of these factors varies from the normal, it is necessary or desirable for the instruments to sense this fact and to initiate corrective action such as closing or opening a valve or giving an indication or alarm, and the like.

Instruments used for control purposes are commonly provided with a lead line such as a hollow tube or the like tapped into the wall of the apparatus at a selected recording or control point. Changes in operating pressure, or pressure differentials, for example, are transmitted to the instrument through these lead lines. In the conversion of heavy hydrocarbon oils by coking, for example, conversion of oil to coke is likely to form deposits which plug or cover these lead lines or taps, and make them operate unsatisfactorily. This is true in varying degrees of other instruments besides those which indicate pressure, all of which may be caused to read, record, or react inaccurately, or not at all, due to deposits of coke and the like. Fluid bed coking reactors are particularly susceptible to clogging and plugging of small taps and lead lines.

It is an object, therefore, of the present invention, to avoid these difficulties. The invention has particular application to fluid bed coking apparatus for conversion of hydrocarbon oils, with attendant production of coke, but it is not limited thereto. It can be used in other apparatus and in connection with various processes, wherever combustible deposits tend to interfere with good instrumentation and control.

Referring to the accompanying drawing which forms a part of this specification, the invention is shown as applied to a fluid bed coking system for the conversion of heavy oils to more volatile products and coke. In such drawings, Fig. 1 shows more or less diagrammatically one form of a coking system in elevation, embodying several control instruments. Fig. 2 is a greatly enlarged fragmentary detail view in section, showing a part of the apparatus at A, in Fig. l, on a much. larger.scale,.to illustrate the application of the invention to sucha system.

The coking system of Fig. 1 comprises a reactorvessel 11 in the form, more or less, of a vertical cylinder, adapted to support a fluidized bed of hot solid particles through which oil to be coked and converted ispassed upwardly. The hot solids, which are preferablylfluidized and preheated in a known manner in another vessel21, flow by gravity through a standpipe 25, controlvalve'27, a U-bend or return bend portion ofconduit29, .a:cut-.oif valve 31 which is normally open, automatic control valve 33 and inlet 35 into reactor 11. Oil feedtmay be.introduced with the hot solids through aline 37 'or at some othersuitable point.

After promoting the coking orthermal conversionroperation in reactor 11 by reason of their high temperature, the spent solids, together with coke formed in the reactor, pass downwardly through stripping conduit 39 where they are stripped by a stripping gas, such as steam, in a well known manner. Part of the solids or product coke may be withdrawn through a line 41. The remainder passes through a return line, with a suitable flow control arrangement such as a U-bend 43, valve 45 and riser 47 back to the heater or burner 21, completing the cycle.

Product vapors from reactor 11 pass overhead through a cyclone 53 where entrained solids are separated and returned to the reactor through a dipleg'SS. The separated vapors leave the cyclone through a product line 57 to suitable recovery equipment, not shown. A pressure recording control valve (PRC) 59 in line 57 is automatically controlled from a lead 61 tapped into the upper part of the reactor.

Within reactor 11, the depth or level of the fluid solids bed is sensed by a level recorder controller (LRC) which operates on taps 63 and 65 at the top and bottom of the reactor. This measures the solids level in the reactor and reacts to control the slide valve 33 as needed.

The difference in pressure between the top of the reactor 11 and the top of the burner or heater 21 is sensed by a diiferential pressure recorder controller device, DPRC, operating through taps 67' and 69. The unit is kept in balance by the automatic control by this device of a valve 71 in the flue gas outlet line of the burner or heater. Other controls, not shown, may be provided where needed.

If any of the taps 61, 63, 65, 67, or 69 should become choked or clogged by coke, ash, or other deposits, it is clear that the system could not operate automatically.

Acordingly, each of the taps is formed as shown in the enlarged detail A, Fig. 2. The tap 65, for example, is tubular, being provided with a slender opening or conduit 81. A T connection 83, or equivalent, provides for attaching an air line 85. A perforated disc or washer 87 is provided with a small perforation 89. This perforation is of such a size that a very small stream of air may constantly flow into the vessel where the tap is mounted, e. g. vessel 11, through the lines 83, 81. This air stream flows inwardly into the vessel and is just sufficient to keep carbon and analogous deposits burned away from the end of the tap 91 which is threaded into the vessel wall. The quantity of air thus supplied is far less than that whichwould have any appreciable effect on the process. In a typical case, an air velocity of 5 ft./sec. through the tap was found to be fully adequate. Air velocity can be as low as 1 ft./sec. or less or up to as much as 20 ft./sec. or more.

While air is preferred, other oxidizing negligible.

3 gases, e. g., mixtures containing 5 to 100% oxygen or equivalent, may be used.

The taps 63, 65, etc., or at least the connected pairs thereof, are preferably indentical in bore and it is preferable to connect the same air line to both so as to neutralize any pressure effects due to the small air stream, even though the air stream is so small that its effect is By supplying air to each tap that is located where deposits might be formed, the control system may readily be kept free of operating difi iculties.

As indicated above, the oxygen or air-fed taps may be used in various ways and in various systems. In some cases other than oxygen or air may be used, even reducing gases in appropriate situations, so long as they react with the deposit-forming material to remove it and prevent the building up of deposits. Obviously, the volume of gas bled in through the taps should never be enough to interfere appreciably with the main process which is 2 being controlled. The gas used for this purpose should 7 be chosen so that no objectionable reaction products are 20 formed in the system, or the quantity of gas supplied that the products thereof, even if objectionable in kind,

2 are not objectionable in quantity.

What is claimed is:

1. In the process of operating a fluid bed coker for the conversion of heavy residual oils, wherein automatic control instrument taps leading into the coker are employed for control purposes, the improvement comprising continuously bleeding into said taps leading into said coker, a small confined stream of oxygen-containing gas at a velocity of about 1 to 20 ft./sec. insufficient to significantly affect the hydrocarbon oil conversion operation while preventing accumulation of carbonaceous deposits in said instrumentation taps.

2, Process of claim 1 wherein the bleed gas is air.

References Cited in the file of this patent UNITED STATES PATENTS 1,470,359 Greenstreet Oct. 9, 1923 1,901,804 Davis et a1. Mar. 14, 1933 2,362,270 Hemminger Nov. 7, 1944 2,390,031 Schutte et al. Nov. 27, 1945 2,561,334 Bowles et al July 24, 1951 2,577,254 Lawson Dec. 4, 1951 2,677,604 Nelson May 4, 1954 

1. IN THE PROCESS OF OPERATING A FLUID BED COKER FOR THE CONVERSION OF HEAVY RESIDUAL OILS, WHEREIN AUTOMATIC CONTROL INSTRUMENT TAPS LEADING INTO THE COKER ARE EMPLOYED FOR CONTROL PURPOSES, THE IMPROVEMENT COMPRISING CONTINUOSLY BLEEDING INTO SAID TAPS LEADING INTO SAID COKER, A SMALL CONFINED STREAM OF OXYGEN-CONTAINING GAS AT A VELOCITY OF ABOUT 1 TO 20 FT./SEC. INSUFFICIENT TO SIGNIFICANTLY AFFECT THE HYDROCARBON OIL CONVERSION OPERATION WHILE PREVENTING ACCUMULATION OF CARBONACEOUS DEPOSITS IN SAID INSTRUMENTATIONS TAPS. 